Masking ability of implant abutment substrates by using different ceramic restorative systems

Information regarding the masking ability of ceramic crowns over different implant abutment materials is scarce.

The purpose of this in vitro study was to evaluate the masking ability of different monolithic or bilayer ceramic materials with different thicknesses over substrates indicated for implant restorations by using opaque and translucent evaluation pastes.

Disk-shaped specimens, shade A1 (VITA Classic; Ø10×1.5 to 2.5 mm), of different ceramics (a bilayer system [yttria-stabilized zirconia infrastructure+porcelain veneer: Zir+Pc] and monolithic systems [lithium disilicate under low, medium, or high translucency: LtLD, MtLD, or HtLD, respectively, and a high-translucent yttria-stabilized zirconia: HtZir]) were made (n=4). The color difference (ΔE₀₀) was assessed by using the CIEDE2000 formula and considering the different ceramic systems over 5 implant abutment materials (A1 shade Zir [Zir A1]; white Zir [White Zir]; A1 low-translucency lithium disilicate [LD]; polyetheretherketone [PEEK]; and titanium [Ti]) when using 2 different evaluation pastes (translucent or opaque). The control comparison was the restorative material positioned over the Zir A1 substrate with a translucent evaluation paste. Statistical analysis was made by using a 2-way ANOVA and Tukey post hoc tests (α=.05) for ΔE₀₀ data considering the restorative material and luting agent factors as their association. Additionally, ΔE₀₀ data were qualitatively analyzed considering the acceptability and perceptibility thresholds. The translucency parameter (TP₀₀) of each restorative material was evaluated, and data were submitted to 1-way ANOVA and Tukey post hoc tests (α=.05).

The most predictable masking ability was seen with Zir+Pc regardless of the evaluation paste used. Nevertheless, under 1.5-mm thickness, Zir+Pc did not adequately mask Ti (ΔE₀₀>1.77). Most monolithic ceramics did not mask discolored substrates (PEEK or Ti, ΔE₀₀>1.77). The exception was HtZir, which presented acceptable masking ability over PEEK at 2.5-mm thickness with both evaluation pastes (ΔE₀₀<1.77). Regardless of the restorative material thickness, Zir+Pc showed the lowest (P<.05) TP₀₀ values (TP₀₀=3.45 at 1.5-mm thickness; TP₀₀=2.00 at 2.5-mm thickness), and HtLD presented the highest (P<.05, TP₀₀=23.50 at 1.5-mm thickness; TP₀₀=13.36 at 2.5-mm thickness). HtZir showed similar TP₀₀ to MtLD at 1.5-mm thickness and similar TP₀₀ to Zir+Pc when used at 2.5-mm thickness (P>.05).

Monolithic ceramics should be used with caution over discolored implant abutments. Bilayer systems (Zir+Pc) were the most predictable approach to adequately masking discolored substrates such as PEEK or Ti. An increased restoration thickness provided higher masking ability for all restorative materials tested.